1. Technical Field
The present invention relates to an image recording apparatus that discharges a radiation-curable ink to form ink dots on a recording medium and cures the ink dots by irradiation so that an image formed by the ink dots will be fixed to the recording medium.
2. Related Art
An ink jet recording apparatus that uses an ultraviolet-curable ink is known as a representative example of this type of image recording apparatus as described in, for example, JP-A-2004-284141 (e.g., FIG. 2 and FIG. 4). Such an ink-jet-recording image recording apparatus discharges droplets of ink through a nozzle provided to a head. The discharged ink droplets make contact with the surface of a recording medium and form ink dots, and then the ink dots spread on the surface of the recording medium. This means that adjacent dots can overlap to a great extent and different colors can be mixed, i.e., what is called bleeding can occur, if the spread of the applied ink is not restricted. Bleeding affects the image quality and also constitutes a main cause of thickened lines. Thus, the ability of ultraviolet-curable ink to cure upon exposure to ultraviolet radiation is used in order that ink dots on the surface of a recording medium should be cured and fixed to the recording medium before spreading farther than necessary.
Irradiating the surface of a recording medium with ultraviolet radiation in such a way requires an ultraviolet irradiation unit. Furthermore, it is needed to irradiate ink dots with ultraviolet radiation before the ink dots spread. From these viewpoints, the above image recording apparatus has an ultraviolet irradiation unit located relatively close to a head. However, the use of this configuration without additional measures can cause clogging as a result of ultraviolet radiation reaching the ejection opening of a nozzle provided to the head and curing the ink existing in the ejection opening. Clogging affects the image quality and is also an obstacle to stable image recording. To solve this problem, the device described in JP-A-2004-284141 has an ultraviolet irradiation unit and a head disposed with the distance between the ultraviolet irradiation unit and the head in a certain range so that ultraviolet radiation should be prevented from reaching the head (an ultraviolet prevention technology).
The device described in JP-A-2004-284141 discharges an ultraviolet-curable ink from a head while transporting a recording medium in a horizontal position with an endless belt stretched between two transport rollers. Another image recording mode is based on the use of a platen drum as described in, for example, JP-A-2011-67964 (FIG. 1). The image recording apparatus described in JP-A-2011-67964 discharges an ultraviolet-curable ink onto the surface of a recording medium wrapped around a platen drum while transporting the recording medium in the direction of the circumference of the platen drum. The ultraviolet prevention technology used in JP-A-2004-284141 cannot be directly applied to this type of apparatus, in which a recording medium is bent while being irradiated with ultraviolet radiation. It is therefore desired to provide a radiation prevention technology suitable for image recording apparatus that record an image with radiation-curable ink, such as ultraviolet-curable ink, while holding up a recording medium with a supporting member that has a curved surface, such as a drum.